1. Field of the Invention
The present invention relates to a system for making electrical connections between an integrated circuit component and a lead frame to which the component is attached, and in particular to a clamp for uniformly securing fingers of variable-sized lead frames in the proper position for bonding of an electrical wire connection thereto.
2. Description of Related Art
In fabricating a semiconductor device, the integrated circuit (IC) component will typically be affixed to a die attach pad at the center of a lead frame, or otherwise stationarily mounted with respect to the lead frame. Thereafter, electrical connections are established between points on the IC component and the individual fingers of the lead frame. As disclosed for example in U.S. Pat. No. 3,806,019 to Diepeveen, wire bonders are known for attaching a first end of an electrically conductive wire to a point on an IC component, and for thereafter attaching a second end of the wire to a selected finger of the lead frame. The ends of the electrical wire may be bonded to the IC component and the individual fingers of the lead frame ultrasonically and/or by heat welding.
FIGS. 1A and 1B show a heater block 24 and clamp 26 supporting an IC component 20 and lead frame 22 during a wire bond process. The clamp 26 is provided to hold individual fingers 22a of the lead frame down on the heater block while a wire 27 is bonded between the IC component and the lead frame. The clamp and heater block fix the position of the IC component and lead frame for the wire bonder, and the heater block further heats the fingers 22a to facilitate the wire bond connection to the lead frame fingers.
It is extremely important that the clamps 26 engage each finger of the lead frame to press the individual fingers against the heater block 24. If the clamp does not hold a particular finger 22a flush against the heater block, unintentional movement of the finger may occur, thereby impeding the ultrasonic weld and preventing good heat transfer from the heater block to the finger. All of this may lead to poor adhesion of the electrical connection on the lead frame finger. A poorly adhered electrical connection may exhibit different electrical conductive properties than other electrical connections. Of further significance, a poorly adhered electrical connection may escape detection during fabrication, and then break once the semiconductor device is operating in a customer's system. Breaking of the electrical connection could cause severe malfunction of the customer's system, and is extremely difficult to locate.
As shown in FIG. 1A, a clamp 26 includes an aperture into which the ends of the lead frame fingers 22a extend, adjacent the IC component 20. Clamp 26 includes a jaw 26a for engaging the ends of the lead frame fingers. Although clamp 26 is shown with a single aperture in FIG. 1A, it is typical that a single clamp may include more than one such aperture so that electrical connections between a plurality of IC components and lead frames may be done in a single wire bonding process. However, it is a severe limitation to conventional wire bond clamps that the temperature and pressure cause the clamps to deform over time. Even slight deformation of the clamp could lead to a poor electrical bond between the IC component and at least some of the lead frame fingers. As shown for example in FIG. 1B, deformation of a clamp 26 can prevent jaw 26a of the clamp from contacting one or more of the lead frame fingers 22a, and thus the finger 22a is not fixed against the heater block. While making the clamp small lessens the degree to which they will deform, using small clamps limits the number of IC component and lead frame pairs which may be electrically connected in a single wire bond process.
Another shortcoming of the prior art relates to the necessity for realignment of the clamp to the lead frame and IC component each time the clamp is changed. IC components, and the open space at the center of a lead frame for the IC components, vary in size. However, conventional wire bond clamps have apertures of a fixed size. Therefore, when it was desired to change the size of the IC component and lead frame, it was necessary to remove the clamp 26 and replace it with a new clamp having apertures appropriate for the new IC component and lead frame. Conventional wire bond clamps have been mounted to the wire bonder by a plurality of screws. In order to replace a wire bond clamp, the screws had to be removed, a new clamp sized for the new IC components and lead frame mounted on the wire bonder, and the screws reapplied. In addition to being time consuming, it has been necessary to realign the clamp to ensure that the X-Y axes are properly aligned to the X-Y axes of the IC component and lead frame. Any misalignment could result in uneven, poor and/or ineffective electrical connections between the IC component and the fingers of the lead frame.
A further disadvantage of conventional clamps that are capable of clamping more than one lead frame at a time is that if the jaws clamping one of the lead frames became damaged, the entire clamp had to be removed and replaced by a new clamp. This is true even if the other jaws of the clamp were not damaged.